The hyperplastic element of prostatic growth involves a net increase in total DNA which is reflected by an enhancement in the rate of DNA synthesis. An animal model has been developed whereby the rate of prostatic DNA synthesis has been correlated with growth and the accumulation of total DNA. This system is applicable to the testing of potential cancer chemotherapeutic agents as well as providing a rapid and precise measurement for determining both the effects of these drugs in vivo and in vitro. Promising cancer chemotherapeutic compounds will be selected and supplied by the National Cancer Institute in conjunction with the National Prostatic Cancer Program. These drugs will be tested in vivo for their ability to inhibit DNA synthesis in the prostatic lobes of castrate rats which are stimulated into growth by treatment with exogenous androgens. Dose response curves will be obtained with each drug and a comparison will be made using the incorporation of three different types of labeled precursors into DNA (H3-thymidine; C14- formate or C14-glycine). The tissue DNA will be isolated and the specific activity determined. The drugs will also be tested for their ability to block the net accumulation of DNA in the dorsal, ventral and lateral lobes of the prostate. It is anticipated that these findings might be informative in making a rational selection of chemotherapeutic agents to be initiated into clinical trials for prostatic cancer.